High strength fastener system

ABSTRACT

A fastener system is constructed wherein the installation and removal drive surfaces intersect an enlarged core diameter in a transitional surface that extends between the installation and removal surfaces of adjacent wings. The transitional surface has a concave form that conforms to the core diameter. The projections of the driver in the system are formed in a blunt shape.

RELATED APPLICATIONS

This application claims priority from Provisional Application for PatentNo. 60/999,874, filed Oct. 22, 2007.

BACKGROUND

1. Field

The disclosed embodiments generally relate to fastener systems includingfastener, driver, method of manufacture and related tooling. Inparticular to fasteners having spiral drive and removal surfaces thatenable high seating torques to be applied.

2. Brief Description of Related Developments

Fasteners having driver engageable surfaces that are, at least in part,defined by spiral segments have been used with good results. Fastenersystems of this type are described in U.S. Pat. Nos. 5,957,645,6,234,914, and 6,367,358 issued to Stacy and commonly owned with thisapplication. The disclosures of these patents are incorporated herein byreference. The drive surfaces of the Stacy fastener system areconstructed to maximize torque transmission, during installation andremoval, while spreading the driving load over a broad driver/fastenerinterface. The thrust of these teachings is to enlarge the area of thedrive surfaces.

More recently certain applications have been found that require theapplication of high seating torques to the fastener. Such torques mayexceed the strength limits of the drivers used to seat the fastener. Itis the purpose of this invention to provide an improved driver/fastenerinterface to increase the available seating torque characteristic of thefastener system.

The problem to which this application is directed, therefore, is toconstruct a drive fastener interface that increases the strength of thedriver without significantly effecting the load distributioncharacteristics of the spiral interface surfaces.

SUMMARY

A fastener system is constructed having driver/fastener interfacesurfaces configured in the general shape of a segment of a spiral onboth of the installation and removal surfaces. The recess and drivercross sectional shapes are constructed with an increased core diameterover the prior art spiral fastener system. This is accompanied by ashortening of the radial extension of the wing of both recess and drivercross sections beyond the core diameter. The wing cross section of thedriver/recess is further modified by moving the installation and removalsurfaces in a parallel manner to form a truncated wing shape with ablunt tip. The blunt tip is constructed to conform to a circle,concentric with the core, with a diameter larger than the core diameter.The drive surfaces are constructed to intersect the core diameter in atransitional surface between the wings that has a concave formconforming to the core diameter.

These changes have resulted in a startling increase in driver strengthand a significant rise in seating torque capability for spiral drivefastener systems. The reduction in drive surface area is offset by theimproved distribution characteristics from the drive surfaces to thecore. To accomplish this the wing portion of the driver/recess crosssection is constructed so that the ratio of the core radius to wing tipradius is greater than 0.55 and the transition surface between the wingsis a concave segment of the core circumference. The ratio of the heightof the wing cross section to its width is constructed to beapproximately equal to or less than 0.5.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the subject matter of this application are explained inthe following description, with reference to the accompanying drawings,in which:

FIG. 1 is a perspective view of a fastener having spirally configureddrive surfaces of the prior art;

FIG. 2 is a perspective view of a driver having spirally configureddrive surfaces of the prior art;

FIG. 3 is a perspective view of an embodiment of a spirally configuredfastener illustrating the subject matter of this application;

FIG. 4 is a perspective view of a spirally configured driverillustrating the subject matter of this application;

FIG. 5 is a chart showing the relative increase in torque capability ofthe fastener system of this application compared to prior art spirallyconfigured fastener systems; and

FIG. 6 is a cross sectional view of an embodiment of a fastener driveraccording to the subject matter of this application with a cross sectionof the prior art driver superimposed shown with dashed outline.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 3 and 4 of this application illustrate, as an example, a fastenerand driver bit of a fastener system having features of an embodiment ofthis application. Although the embodiments disclosed will be describedwith reference to the drawings, it should be understood that they maytake many alternate forms.

A fastener system 1, according to the subject of this application, isshown in FIGS. 3 and 4 and consists of fastener 2 and driver bit 3.Fastener 2 is constructed having a head 4 and a threaded shank 5. Aspirally configured recess 6 is formed in head 4. Driver bit 3 isconstructed having spirally configured drive surfaces that mate with thecorresponding surfaces of fastener recess 6. As shown in the example ofFIG. 4, driver bit 3 utilizes a generally cruciform shape having wings 7a,b,c, and d. Similarly to prior art spirally configured fasteners, theoverall shapes and number of wings may be varied from the exampleillustrated. Each of the wings have a substantially similar shape withan installation surface 8, a tip portion 11 and a removal surface 9 thatdefine the wings 7. A transition surface 10 extends between theinstallation and removal surfaces of adjacent wings, such as wings 7 aand 7 b as shown in FIG. 4. The overall shape of the recess 6 and driverbit 3 is similar, except the bit 3 is smaller to provide a clearancebetween driver and fastener to promote engagement and removal of thedriver bit 3 from the recess 6. In addition the driver bit installationand removal walls are slightly different from the corresponding recesswalls so rotation of the bit will provide a full face to face engagementon both the removal and installation wall. As indicated above, thedriver/fastener interface surfaces are configured in the general shapeof a segment of a spiral on both of the installation and removalsurfaces.

The details of the recess and driver bit shape are shown in FIG. 6. Forsimplicity only a cross sectional view of a driver is provided, it beingunderstood that the recess is similarly shaped as shown in FIG. 3.Although the engagement surface of the fastener head 4 are shown to berecessed to receive a mating male configured driver, it is equallypossible to provide the engagement surfaces as external surfaces of head4 for engagement with a female configured driver, as shown in FIGS. 13and b of the '358 patent incorporated herein by reference.

FIG. 6 illustrates a cross section of an embodiment of driver 3 with across section of a prior art driver 34 in phantom, as shown in FIG. 2.It is observed that the cross sectional shape of driver 3 is constructedwith an increased core radius (R₂) over the prior art spiral driver 34(R₂′). The overall radius R₁ remains unchanged, thereby requiring ashortening of the height h of wing 7 in order to accommodate theenlarged core radius R₂. This results in a reduced surface area for thedriving surfaces with an anticipated deficit to performance. The crosssection of wing 7 is further modified by moving the installation andremoval surfaces 8 and 9 outward in a parallel manner to form atruncated wing shape with a blunt tip 11. The blunt tip 11 isconstructed to conform to a segment of a circle, concentric with thecore 12, having a diameter larger than the core diameter. The drivesurfaces 8 and 9 are constructed to intersect the core diameter in atransitional surface 10 between adjacent wings, for example, wings 7 aand 7 d with transitional surface 10 d. The transitional surface 10 hasa concave form that conforms to the core diameter.

As shown in FIG. 6 a cross section of driver 3 is shown having wings orprojections 7 a,b,c,d. The wings are defined respectively byinstallation drive surfaces 8 a,b,c,d, tip contours 11 a,b,c,d, andremoval drive surfaces 9 a,b,c,d. Adjacent wings intersect the corecircumference 12 in transitions surfaces 10 a,b,c,d. For comparison, theprior art driver 34 is shown in phantom having wings 40 extendingoutward from a core with a radius (R₂′) and defined by installationdrive surfaces 46 and removal drive surfaces 48.

Instead of a deficit in performance, these changes have resulted in astartling increase in driver strength and a significant rise in seatingtorque capability for spiral drive fastener systems. The reduction indrive surface area is offset by the improved distributioncharacteristics from the drive surfaces to the core. FIG. 5 is a chartof test results showing the results of bit strength tests performed onthe high strength bit of the fastener system of this application and thesame size bit of the prior art spirally configured fastener systems. Theincreased strength, represented in the chart of FIG. 5, is indicative ofthe significant advantage provided by the fastener system of thisapplication.

The increased strength of the system and the increased seating torque,may be attributed to the recess and driver being constructed with a corediameter that is increased over the prior art spiral fastener system. Itwould have been logical to try to maintain the area of the drivesurfaces by constructing the transition surface as a convex continuationof the installation and removal surfaces 7 and 8 similar to the priorart design as shown in FIG. 6 by phantom line 50. Instead according tosubject matter of this application, the drive surfaces 8 and 9 areconstructed to intersect the core diameter in a transitional surface 10between the wings 7 that has a concave form conforming to the corediameter. This adds to core strength, but further truncates the wingcross section and reduces drive surface area. In addition, by truncatingthe outer tip of the wing cross section and moving the drive surfacesoutward in parallel with the prior art configuration, the wing may beenlarged and formed with a blunt tip, the strength of the system maybefurther increased. It is observed that the center of mass of the wingwill also be moved outward, thereby effecting an improved loaddistribution.

This is accompanied by a shortening of the radial extension of the wingof both recess and driver cross sections beyond the core diameter. Thewing cross section of the driver/recess is further modified by movingthe installation and removal surfaces in a parallel manner to form atruncated wing shape with a blunt tip. The blunt tip is constructed toconform to a circle, concentric with the core, with a diameter largerthan the core diameter.

To accomplish this the cross section of the wing portion of the driver 3(and therefore also the wing portion of the recess 6) is truncated bothoutward from the core circumference 12 and inward from the tip 11. Inthis manner, the projections 7 are constructed so that the ratio of coreradius R₂ to the wing tip radius R₁ is greater than 0.55 and thetransition surface 10 between the wings 7 is a concave segment of thecore circumference. Preferably the ratio of R₂/R₁ is in the range of0.65 to 0.70. In addition the width w of the wings or projections 7a,b,c,d, is enlarged while maintaining the profile of the drive surfacesto be consistent with the prior fastener system. The ratio h/w of theheight h of the wing cross section to its width w is constructed to beapproximately equal to or less than 0.5. In comparison, referring toFIG. 6, the ratio R′₂/R₁ may be calculated to be approximately 0.46 andthe ratio of prior art fastener systems (h′/w′) may be calculated to beapproximately 0.93. These modified dimensions have proven to provide asignificant advantageous improvement in bit strength.

Although the subject matter of this application is discussed withreference to a fastener system having spirally configured drivesurfaces, it is believed that the construction and method is equallyapplicable to other cruciform style fastener systems, in particular, ahexalobular style fastener system as described in U.S. Pat. No.6,017,177 and ISO 10664.

In this manner a new and unique fastener system is presented thatprovides a startling improvement in strength characteristics withrespect to the driver without a deficit to the overall performance ofthe fastener system.

It should be understood that the above description is only illustrativeof the invention. Various alternatives and modifications can be devisedby those skilled in the art with out departing from the invention.Accordingly, the present invention is intended to embrace all suchalternatives, modifications and variances which fall with the scope ofthe appended claims.

1. A fastener system comprising: a fastener having a head and a shankwherein the head is constructed having driver engageable surfaces andsaid driver engageable surfaces define multiple wings radially extendingfrom a central core; a driver having a bit end constructed with matingsurfaces for engagement with the driver engageable surfaces of therecess in the fastener head and said mating surfaces define multipleprojections radially extending from a central core matching the wings;wherein each of said projections are constructed with a cross sectionalshape comprising an installation surface, a tip portion and a removalsurface that define the projection, and wherein each of the projectionsare connected by a transition surface extending between the installationand removal surfaces of adjacent projections and where the transitionsurface conforms to a circumference of the central core; wherein thecross sectional shape comprises a projection having a width and a heightand the ratio of the projection height to the projection width is equalto or less than 0.5; and further wherein the driver engageable surfacesof the fastener head are constructed to receive the mating surfaces ofthe driver.
 2. A fastener system according to claim 1 wherein the crosssectional shape comprises a central core having a first radius and a tiphaving a second radius and wherein the ratio of the first radius to thesecond radius is greater than 0.55.
 3. A fastener system according toclaim 2 wherein the ratio is greater than 0.65.
 4. A fastener systemaccording to claim 1 wherein the cross sectional shape comprises acentral core having a first radius and a tip having a second radius andwherein the ratio of the first radius to the second radius is within therange of 0.65 to 0.70.
 5. A fastener system according to claim 1 whereinthe driver engageable surfaces are constructed in the shape of a spiralsegment and said mating surfaces have a matching shape.
 6. A fastenersystem, according to claim 1 wherein the projections are arranged in anhexalobular configuration.
 7. A method of constructing a fastener systemcomprising: forming a fastener having a head and a shank wherein thehead is constructed having driver engageable surfaces and said driverengageable surfaces define multiple wings radially extending from acentral core; constructing a driver having a bit end having matingsurfaces for engagement with the driver engageable surfaces of thefastener head and said mating surfaces define multiple projectionsradially extending from a central core matching the wings; constructingeach of said projections with a cross sectional shape comprising aninstallation surface, a tip portion and a removal surface that definethe projection, and wherein each of the projections are connected by atransition surface extending between the installation and removalsurfaces of adjacent projections and where the transition surfaceconforms to a circumference of the central core; truncating each of theprojections from the core outward and from the tip portion inwardthereby forming each of the projections having a width and a height andthe ratio of the projection height to the projection width is equal toor less than 0.5; and forming the driver engageable surfaces of thefastener head to receive the mating surfaces of the driver.
 8. Themethod according to claim 7 further comprising forming the central corehaving a first radius and the tip portion having a second radius andwherein the ratio of the first radius to the second radius is greaterthan 0.55.
 9. The method according to claim 8 wherein the ratio isgreater than 0.65.
 10. The method according to claim 7 furthercomprising forming the central core having a first radius and the tipportion having a second radius and wherein the ratio of the first radiusto the second radius is within the range of 0.65 to 0.70.
 11. The methodaccording to claim 7 wherein the driver engageable surfaces areconstructed in the shape of a spiral segment and said mating surfaceshave a matching shape.
 12. The method according to claim 7 wherein theprojections are arranged in an hexalobular configuration.
 13. A fastenersystem comprising: a fastener having a head and a shank wherein the headis constructed having driver engageable surfaces and said driverengageable surfaces define multiple wings radially extending from acentral core; a driver having a bit end constructed with mating surfacesfor engagement with the driver engageable surfaces of the recess in thefastener head and said mating surfaces define multiple projectionsradially extending from a central core matching the wings; wherein eachof said projections are constructed with a cross sectional shapecomprising an installation surface, a tip portion and a removal surfacethat define the projection, and wherein each of the projections areconnected by a transition surface extending between the installation andremoval surfaces of adjacent projections and where the transitionsurface conforms to a circumference of the central core; wherein thedriver engageable surfaces of the fastener head are constructed toreceive the mating surfaces of the driver; and further wherein thedriver engageable surfaces are constructed in the shape of a spiralsegment and said mating surfaces have a matching shape.
 14. A method ofconstructing a fastener system comprising: forming a fastener having ahead and a shank wherein the head is constructed having driverengageable surfaces and said driver engageable surfaces define multiplewings radially extending from a central core; constructing a driverhaving a bit end having mating surfaces for engagement with the driverengageable surfaces of the fastener head and said mating surfaces definemultiple projections radially extending from a central core matching thewings; constructing each of said projections with a cross sectionalshape comprising an installation surface, a tip portion and a removalsurface that define the projection, and wherein each of the projectionsare connected by a transition surface extending between the installationand removal surfaces of adjacent projections and where the transitionsurface conforms to a circumference of the central core; forming thedriver engageable surfaces of the fastener head to receive the matingsurfaces of the driver; and further wherein the driver engageablesurfaces are constructed in the shape of a spiral segment and saidmating surfaces have a matching shape.
 15. A fastener system comprising:a fastener having a head and a shank wherein the head is constructedhaving driver engageable surfaces and said driver engageable surfacesdefine multiple wings radially extending from a central core; a driverhaving a bit end constructed with mating surfaces for engagement withthe driver engageable surfaces of the recess in the fastener head andsaid mating surfaces define multiple projections radially extending froma central core matching the wings; wherein each of said projections areconstructed with a cross sectional shape comprising an installationsurface, a tip portion and a removal surface that define the projection,and wherein each of the projections are connected by a transitionsurface extending between the installation and removal surfaces ofadjacent projections and where the transition surface conforms to aconcave circumference of the central core; wherein the cross sectionalshape comprises a central core having a first radius and a tip having asecond radius and wherein the ratio of the first radius to the secondradius is greater than 0.55; and further wherein the driver engageablesurfaces of the fastener head are constructed to receive the matingsurfaces of the driver.
 16. A method of constructing a fastener systemcomprising: forming a fastener having a head and a shank wherein thehead is constructed having driver engageable surfaces and said driverengageable surfaces define multiple wings radially extending from acentral core; constructing a driver having a bit end having matingsurfaces for engagement with the driver engageable surfaces of thefastener head and said mating surfaces define multiple projectionsradially extending from a central core matching the wings; constructingeach of said projections with a cross sectional shape comprising aninstallation surface, a tip portion and a removal surface that definethe projection, and wherein each of the projections are connected by atransition surface extending between the installation and removalsurfaces of adjacent projections and where the transition surfaceconforms to a concave circumference of the central core; forming thecentral core having a first radius and the tip portion having a secondradius and wherein the ratio of the first radius to the second radius isgreater than 0.55; and forming the driver engageable surfaces of thefastener head to receive the mating surfaces of the driver.